1. Field of the Invention
The present invention relates to an air pressure detection device for wheel for detecting the air pressure of a tire and making it possible for the driver to recognize the air pressure of the tire even during running of the vehicle.
2. Description of Background Art
An air pressure detection device for a wheel which enables the driver to recognize the air pressure of a tire even during the operation of the vehicle is known, for example, as disclosed in Japanese Unexamined Patent Publication No. Hei 1044726, “Tire Air Pressure Alarm Device.”
Japanese Unexamined Patent Publication No. Hei 10-44726 discloses a tire air pressure alarm device in which, according to FIG. 1 of the publication, a valve stem 10 (symbols used in the publication are used here) is provided that is fitted to a wheel rim 1. A case 2 is disposed at a lower portion of the valve stem 10. A transmission unit 7 includes a pressure detecting portion 3, a signal processing circuit 4 and an electric cell 5 that are contained in the case 2.
However, since the above tire air pressure detection device is designed so that the pressure detecting portion 3, the signal processing circuit 4 and the electric cell 5 are contained in the case 2, which is fitted to a lower portion of the valve stem 10, it is difficult to exchange the electric cell when, for example, the life of the electric cell is shorter than the tire exchange interval.
This disenables effective utilization of the air pressure detection device, even though the device can detect the air pressure of the tire during operation of the vehicle. Namely, there is a demand for an air pressure detection device for wheel which can facilitate the exchange of the electric cell.